This Android power feature gave Google a privacy headache

A Google experiment to extend battery life has landed Android in privacy hot water, with concerns that devices running the OS have been sending details of nearby cell towers to the company's servers. Although Google insists that the data not only was handled entirely separately from any of the location services visible to third-party apps, and indeed its own advertising activities, it has confirmed it will nonetheless be ending the trial. The hiccup once again highlights the at-times difficult balance between maximizing device performance while ensuring essential services act as users expect them to.

The issue, first reported by Quartz, saw a third data point appended to the usual two that all Android cellphones regularly transmit to ensure message routing. Mobile Country Codes (MCC) and Mobile Network Codes (MNC) concern which country a user is and what network they're currently active on, respectively. Those details are used so that messages sent to a user are correctly delivered.

What Google considered adding was Cell ID, the code for the specific cell tower that the device was connected to, to its Firebase Cloud Messaging system that manages MCC and MNC. That would have had some clear advantages, since Google could have used it to control how often the phone sent a so-called "heartbeat" signal to the network to say that it was still active. Cutting down those regular heartbeats could save on battery life, so the theory went: some mobile networks need a more frequent ping else messages aren't delivered correctly, while others can go longer between those check-ins.

Get the balance right, and you could maximize power management without sacrificing performance. As a result, Cell ID transmission was switched on in January 2017. In a statement provided to SlashGear, a Google spokesperson confirmed that Cell ID had been transmitted, though insisted that the data was never actually saved by Google nor provided to carriers:

"To ensure messages and notifications are received quickly, modern Android phones use a network sync system that requires the use of Mobile Country Codes (MCC) and Mobile Network Codes (MNC). In January of this year, we began looking into using Cell ID codes as an additional signal to further improve the speed and performance of message delivery. However, we never incorporated Cell ID into our network sync system, so that data was immediately discarded, and we updated it to no longer request Cell ID. MCC and MNC provide necessary network information for message and notification delivery and are distinctly separate from Location Services, which provide a device's location to apps." Google

As Google describes it, though the Firebase Cloud Messaging system had support for Cell ID, it was never actually integrated into the heartbeat system. Any Cell ID data sent from a device to Google was rejected by the server. MCC and MNC data is briefly stored by Google after being used, then purged.

Cell ID transmission has now been given the instruction to shut down. However, though Google made that decision last week, it's only when devices perform their regular, intermittent check-in for security updates that they'll be notified to stop transmitting. It's expected to take a couple of weeks to fully propagate, and likely be complete by the end of the month.

Location tracking has become a hot-button topic as smartphones become more central to users' lives, and the value of positioning data grows. Certainly, had Google fed Cell ID information into its Location Services system, which can be accessed by third-party apps and services, that would be a considerable point of concern. As it stands, however, Google says Cell ID not only wasn't used for any commercial reason or passed on to carriers, but the company itself never actually collected it.